1. Field of the Invention
The present invention relates to an electrophotographic recording apparatus to form, on a charge carrying drum namely on a photoconductive or dielectric image carrier, electrostatic latent images from data as supplied in a form of electric signals from information processing apparatuses such as the electronic computer with use of an electrostatic recording head such as an optical fiber tube and to develop visible images from these electrostatic latent images by an electrophotographic process for recording in copy sheets wherein a gap between the recording head and the image carrier may be readily checked at high accuracy.
2. Description of the Prior Art
Electrophotographic data recording apparatuses have recently been developed and are being applied for use as the computer terminal, output device for data transmitted through communication lines, output printing unit of facsimile system, etc. Examples of the above electrostatic recording head that transforms electric signals into image patterns are the optical fiber tube, cathode ray tube, and needle electrode. By way of example, the optical fiber tube (hereinafter referred to as "OFT") is used in the following description.
The image quality including focusing condition, and size, uniformity and sharpness of copy characters is much affected by the gap between the tip of OFT and the photoconductive image carrier. For example, in case of a wide gap, copy characters are often blurred and much distorted. Therefore, it is very important to this type of equipment to accurately adjust the gap between the tip of OFT and the photoconductive image carrier. Since this gap is narrow and 100 to 500 .mu.m wide, its adjustment is rather difficult and requires much time. If the photoconductive image carrier is provided in a form of drum, the gap sometimes fluctuates, with the tip of OFT and the surface of photoconductive touching each other in extreme cases, depending on eccentricity of drum, allowance on its mount position, etc., so it is necessary to check the gap along the whole circumference of drum. Though the above gap 100 to 500 .mu.m wide can be checked, for example, by a method making use of a thickness gauge, it has been found from results of various experiments that looking through the gap is the best check method.